HELP!!!!!!!!!!!!!!!!!

Answer:
To do this I am pretty sure your going to have to do some hard calculations.
Lets go deeper
so because it is a rectangle every angle is a right angle according to the property of a rectangle.
A right angle is 90 degress
So 8x+18=90
90-18=72
8x=72
72/8=9
x=9
Feel free to do brainlest if correct